This patent application claims priority of International Application No. PCT/CB98/01938, filed on Jul. 1, 1998 (01.07.98).
This invention relates to apparatus and methods for gas sampling, with particular refer to gas sampling in hand-held portable gas sensing devices.
Devices which can detect a range of gases (so-called xe2x80x9celectronic nosesxe2x80x9d) have recently become commercially available. Such devices typically comprise an array of individual gas sensing elements, the elements having broad and overlapping sensitivities. The identity of a gas is established by reference to the pattern of response across the array of sensors (see, for example, Gardner J W and Bartlett P N, Sensors and Actuators B, 18-19 (1994) 211-220; Persaud K C, Bartlett J G and Pelosi P. in xe2x80x98Robots and Biological Systems: Towards a new bionics?xe2x80x99, Eds. Dario P, Sandini G and Aebisher P. NATO ASI Series F: Computer and Systems Sciences 102 (1993) 579 and references therein).
Electronic noses have to date generally comprised bench-top units, usually interfaced to a personal computer which performs pattern recognition functions and data processing. Such devices are perfectly convenient for use in a laboratory, but are not portable and therefore not suitable for use in the field. It is likely that the next generation of electronic noses will include portable, hand-held devices. One problem with the production of a practical, hand-held electronic nose is the gas sampling system. Conventional bench-top electronic noses utilise small pumps to draw a stream of gas across the gas sensor array. It is less desirable to employ such an approach in a hand-held device, because of the additional requirements placed upon the battery power source, with consequential and unacceptable increases in the weight and volume of the instrument.
The present invention addresses the above named problem.
Although primarily directed towards electronic noses, the present invention has within its scope other hand-held gas sensing devices, including gas specific, single sensor devices.
For the avoidance of doubt, the term xe2x80x9cgasxe2x80x9d is understood to embrace any ambient atmosphere, which might comprise a mixture of gases and/or vapours.
According to a first aspect of the invention there is provided a gas sampling apparatus adapted for use in a hand-held gas sensing device having at least one gas sensor, the apparatus comprising:
gas inlet means;
gas conducting means for conducting gas from said gas inlet means to the sensor or sensors;
gas outlet means;
gas conducting means for conducting gas from the sensor or sensors to the gas outlet means; and
vacuum containment means enclosing an inner region having a pressure below atmospheric pressure and adapted for connection to the gas outlet means so that a flow of gas is developed from the gas inlet means to the vacuum containment means.
The apparatus may further comprise pressurised wash gas containment means containing a wash gas and adapted for connection to the gas outlet means so that a flow of wash gas is developed across the gas sensor or sensors.
The apparatus may further comprise pressurised reference gas containment means containing a reference gas and adapted for connection to the gas outlet means so that a flow of reference gas is developed across the gas sensor or sensors.
The gas outlet means and/or the gas inlet means may comprise valve means.
The vacuum containment means may comprise valve means.
The apparatus may further comprise gas flow constriction means.
According to a second aspect of the invention there is provided a method for sampling gas in a hand-held gas sensing device having at least one gas sensor comprising the steps of:
providing apparatus according to the first aspect of the invention; and
connecting the vacuum containment means to the gas outlet means so that a flow of gas is developed from the gas inlet means to the vacuum containment means.
The step of connecting the vacuum containment means to the gas outlet means may be preceded by the steps of:
connecting pressurised reference gas containment means containing a reference gas to said gas outlet means so that a flow of reference gas is developed across the gas sensor or sensors.
This step comprises a xe2x80x9creference cyclexe2x80x9d.
The step of connecting the pressurised reference gas containment means may be preceded by the step of:
connecting pressurised wash gas containment means containing a wash gas to said gas outlet means so that flow of wash gas is developed across the gas sensor or sensors.
This step comprises a xe2x80x9cwashxe2x80x9d cycle.
The method may further comprise the steps of gas tightly sealing the vacuum containment means; detaching same from the gas outlet means; and transporting said vacuum containment means to secondary analysis means for further analysis of the sampled gas.